764 Proceedings of Royal Society of Edinburgh. [sess. 
On the surface of the sub-umbrella there are a number of fine 
lines (about three to five between every two radial canals) which 
extend from the stomach to the margin of the umbrella. Many 
of the lines bifurcate near the stomach, and also near the margin 
of the umbrella. Occasionally a line has two or three branches, 
and even a slight anastomosing with an adjacent line occurs. In 
large adult specimens lines were found which only proceeded a 
short distance from the margin of the umbrella towards the 
stomach. 
Romanes (1876) noticed these lines, and regarded them as 
longitudinal muscle-bands. Hartlaub (1894) states that they bear 
a resemblance to streaks of nematocysts. I also am inclined to the 
view that they are nematocyst-tracks. 
Romanes ( 1 87 6), in his description of Stomobrachium octocostatum 
found in Cromarty Firth, pointed out that his specimens were not 
quite like those described by Forbes, and he regarded them as a 
distinct variety. The tentacles are arranged in a double series ( i.e . 
long and short tentacles alternating with one another), and not in 
a single series as figured by Forbes. Now, Forbes has given his 
own figure, but the description is partly based upon Ehrenberg’s 
account of the species, and the alternating series of large and 
small tentacles is mentioned by Forbes on the authority of 
Ehrenberg. Forbes clearly states that he did not thoroughly 
examine his specimens, for he says, — “I have not met with (it) 
since my first season’s study of medusae in 1839, when, though I 
made a careful drawing of it, I did not examine its minute 
structure, trusting to meet with it again, as it seemed to be one of 
the most abundant of its tribe.” There can be no doubt that 
Forbes overlooked the small tentacles when drawing the specimen 
while on his yachting cruise. 
On the Genera Melicertum and Melicertidium. 
According to Haeckel’s classification, Oceania ( Stomobrachium ) 
octocostata , Sars, belongs not to the genus Melicertidium but to the 
genus Melicertum. The genus Melicerta was established by Peron 
(1809), and the spelling was changed to Melicertum by Oken 
(1815). One of the species in this genus was Medusa campanula 
